I. Soutar

Transient decay studies of photophysical processes in aromatic polymers: 2. Investigation of intramolecular excimer formation in copolymers of 1-vinyl naphthalene and methyl acrylate

Abstract Transient decay studies of the copolymer system 1-vinyl naphthalene/methyl acrylate using pulsed laser excitation have shown that monomer and excimer decay rates are not described by dual exponential functions. Triple exponential decays are attributed to the existence of emission from two kinetically distinct monomer sites in addition to that of the excimer. Variation of intramolecular chromophore concentration in the copolymers allows adoption of a versatile series of extrapolation procedures to derive individual rate constants in the photophysical reaction scheme governing intramolecular excimer formation. Use of this procedure yields a rate parameter governing excimer formation in which the dependence upon local chromophore concentration within the polymer coil is removed to a degree not possible in studies of homopolymers alone.

Fluorescence depolarization studies of micro-brownian relaxations of poly (methyl methacrylate) in solution

Abstract Fluorescence depolarization and quenching measurements have been used to study motions of poly(methyl methacrylate) in toluene at 298 K. Data concerning segmental motion of the polymer chain have been obtained using both an “ideal” label which cannot move independently of the macromolecule and a label in which independent motion should not result in depolarization of radiation. The results compare favourably. Motions affecting the ester group and terminal macromolecular segments also have been studied. The use of naphthalene derivatives as labels of limited bulk has been made possible by the use of dynamic quenching.

Fluorescence quenching and polarization studies of segmental motion in polystyrene

Abstract Fluorescence quenching has been used in conjunction with measurements of fluorescence polarization to study the segmental relaxation of polystyrene. There is confirmation of the apparent variation in the intrinsic polarization of the bound fluorescent probe with the nature of the macromolecule. The results agree with previous observations, using a different fluorescence approach, that the rotational times for groups at the chain ends are less than one fifth of those for the same groups in the chain interiors. The variation of intrinsic polarization with polymer structure is discussed.

Polymerization by alkaline earth metal compounds—I. Studies on the polymerization of methylmethacrylate by triphenylmethyl metal derivatives and related compounds of calcium, strontium and barium

Abstract A series of related organo-alkaline earth metal compounds of formula (Ph3C)MX(THF)η, (M = Ca, Sr, Ba; X = Cl: M = Ca, Sr; X = Br: M = Ba; X = CPh3), has been isolated and characterized using analytical and spectroscopic techniques. The polymerization of methylmethacrylate (MMA) has been studied using these organometallic compounds as initiators. Investigations of the tacticity variations of polymethylmethacrylate (PMMA) produced in 1,2-dimethoxyethane or tetrahydrofuran (THF) at 210 K have shown that the syndiotacticity is higher in the former solvent, decreases with the following changes in initiator composition: Ca > Sr ⩾ Ba; Cl > Br; in THF, it is dependent on the monomer concentration. The molecular weight distributions of the PMMA samples are broad and have distinct bi- or poly-modal features. The polymerization process appears to be anionic in nature but the evidence suggests that more than one type of propagation occurs and mechanistic aspects are discussed. Polymerization of bulk MMA by these same initiators is also reported. The initiators RMX(THF)n (M = Sr, R = Me, n = 3 or R = Et, n = 2) and (C3H5)SrBr(THF)2 are shown to be inefficient for polymerization of MMA. The glass transition temperatures of a range of PMMA samples of differing tacticity are presented and discussed.

Intramolecular excimer formation in macromolecules—V. Head-to-head polystyrene, block copolymers of styrene and butadiene and regular condensation polymers of α-methylstyrene

Abstract Studies of the photophysical properties of head-to-head polystyrene, block copolymers poly(butadiene- b -styrene) and polystyrenes of various sequence length of styrene chromophore and regular copolymers of α-methylstyrene indicate that interactions between phenyl chromophores located distantly upon the macromolecule are not of major significance in determination of excimer formation in styrene polymers. It is concluded that intramolecular excimer formation in polystyrenes occurs primarily as a consequence of interactions between nearest neighbour chromophores in the polymer chain. The influence of polymer coil dimensions upon intramolecular excimer formation is demonstrated. The photophysical behaviour of poly(butadiene- b -styrene) block copolymers shows the importance of intramolecular energy migration in population of potential excimer sites.

Transient decay studies of photophysical processes in aromatic polymers—III. Concentration dependence of excimer formation in copolymers of acenaphthylene and methyl methacrylate

Abstract The fluorescence behaviour of a series of acenaphthylene/methyl methacrylate copolymers covering a wide range of intramolecular chromophore compositions has been examined using pulsed laser excitation. The decay of emission intensity in the region of monomer fluorescence could be described only by the use of triple exponential functions. The data have been discussed in terms of the existence of two temporally distinct monomeric species in addition to an excimer.

Intramolecular excimer formation in macromolecules—IV: Energy migration and excimer formation in copolymers of acenaphthylene and methyl acrylate

Abstract Energy migration and intramolecular excimer formation have been examined in copolymers of 1-vinylnaphthalene and methyl acrylate. The degree of depolarization of fluorescence, p −1 from glassy solutions of the copolymers in 2-methyltetrahydrofuran at 77 K was used to characterize the extent of intramolecular energy migration which is described by the mean sequence length of naphthalene chromophores, l n . The proportionality of the ratio of excimer to monomer intensities of emission to the function l n · f nn implies that the excimer site concentration is proportional to the fraction of naphthalene pairs, f nn , in the copolymer. The same function has been shown previously to describe intramolecular excimer formation in 1-vinylnaphthalene/methyl methacrylate and other copolymers [20, 21]. Comparison of the data pertinent to the methyl acrylate copolymers with those of the methyl methacrylate series shows that (a) there is no evidence for long range intramolecular excimer formation in copolymers of vinylaromatic chromophores even in the relatively flexible methyl acrylate series; (b) intramolecular excimer formation, occurs more readily in the less sterically constrained methyl acrylate series consequent upon the fact that rotation into the excimer conformation will be less restricted and that (c) energy migration is more extensive in the methyl acrylate copolymers. It has been demonstrated that comparison of excimer formation efficiency in different copolymer systems is more meaningful when a common value of the function descriptive of the formation is used as opposed to a common chromophore concentration. Reactivity ratios of 1-vinylnaphthalene and methyl acrylate were determined as 1.18 and 0.39 respectively.

Polymerization by alkaline earth metal compounds—II Polymerization of 2- and 4-vinylpyridine, styrene and butadiene by triphenylmethyl derivatives of calcium, strontium and barium

Abstract Investigations are reported on polymerizations of 2- and 4- vinylpyridine, styrene and butadiene by a series of related alkaline earth metal initiators, Ph 3 CMX(THF) n (M = Ca, Ba, X = Cl, n = 2; M = Ca, X = Br, n = 4; M = Sr, X = Cl, n = 4; M = Sr, X = Br, n = 5) in tetrahydrofuran (THF) or 1,2-dimethoxyethane (DME) at various temperatures and in the absence of solvent. The polymers have been examined by GPC and aspects of their microstructures determined by 13 C and/or 1 H NMR spectroscopy and, for polybutadiene, i.r. spectroscopy. Poly-2-vinylpyridine produced by Ph 3 CMX(THF) n is rich in isotactic content; the isotacticity is higher for polymer formed in THF than DME solution, falls with change of initiator in the order M = Ca > Sr > Ba and, in DME, is greater when X = Br. The tacticities of poly-4-vinylpyridine and polystyrene are similar to those obtained from related organometallic initiators. The 1,4-content of polybutadiene decreases with initiator Ph 3 CMX(THF) n in the order M = Ba > Sr > Ca; the trans -1,4 structure generally predominates except when M = Ba from which cis -1,4 links are formed in comparable amounts.

The preparation and characterization of phosphorus-terminated poly-1,3-butadiene: new telechelic ionomers

Polybutadienyllithium systems, with high 1,4-microstructure, low polydispersity and Mn in the range (2–10) × 103, have been produced in hydrocarbon solvents by using n-butyllithium or 3-dimethylamino-propyllithium as initiator. Termination of these ‘living’ polymers with chlorophosphine, ClPR2 (R = Ph, Et or Cy), occurs to give oxidatively unstable phosphine derivatives Y-(C4H6)n-PR2, in up to 93% efficiency. Oxidation products include the related phosphine oxides. Quaternization of the phosphinated polymers in situ with iodomethane gives a quantitative conversion into the cationomeric polymers Y′-(C4H6)n-PR2Me+I−, including the novel dicationic telechelic systems with Y′ = I+NMe3(CH2)3, which show thermoplastic elastomeric properties. The products have been characterized by gel permeation chromatography, end-group analysis and 1H, 13C and 31P nuclear magnetic resonance spectroscopy. Model quaternary phosphonium derivatives, trans- and cis-t-BuCH2CHCHCH2PR2Me+I− and t-BuCH2CH(CHCH2)PR2Me+I−, are reported and help establish the terminal geometry of the quaternary phosphonium-capped polybutadienes: the addition of phosphorus to the terminal butadienyl follows the order cis-1,4>trans-1,4>1,2 with the amount of 1,2-termination being smallest when R is the bulky cyclohexyl group.

The effect of transient quenching on the excimer kinetics of 2,5-diphenyloxazole

Abstract Excimer formation in 2,5-diphenyloxazole (PPO) in ethanol is shown not to obey the expected biexponential kinetics because of the presence of time-dependent quenching. Between 25 and 50°C the decay of monomer fluorescence can be described by a model based on the linear superposition of excimer reverse dissociation and transient quenching to give values for the diffusion coefficient and the interaction radius. However, at lower temperatures the model provides an incomplete description and the indications are that this is caused by the emergence of a heterogeneous distribution of PPO molecules.