Richard H. Still

THERMAL, MECHANICAL AND FRACTURE PROPERTIES OF REACTION INJECTION-MOULDED POLY (URETHANE-UREA)S

Abstract A series of poly(urethane-urea)s similar to those used commercially (formed from a 4,4′-diphenylmethane diisocyanate-based polyisocyanate and a polyether triol in admixture with an aromatic diamine, 3,5-diethyltoluenediamine) were prepared, with appropriate catalysis over a wide range of composition, by reaction injection moulding (RIM). All reactants were thoroughly characterized prior to use and the polymers were formed on in-house RIM equipment under controlled processing conditions. The RIM materials formed ranged from translucent flexible elastomers to opaque rigid plastics depending on their composition and were characterized by dynamic mechanical thermal analysis (d.m.t.a.), tensile stress-strain and fracture mechanics studies. D.m.t.a. showed that (micro)phase separation had occurred during polymerization and the RIM materials had a non-equilibrium two-phase morphology. The modulus data from the tensile stress-strain studies were compared to the predictions of theories for two-phase materials. The comparative data showed good agreement, over a wide range of composition, to a model for materials comprising a co-continuous morphology. Fracture properties were determined using a single edge notch technique. Low hard-segment materials failed in a ductile manner accompanied by gross tearing, as observed on scanning electron microscopy fracture surfaces, with values of critical strain energy release rate, GIC > 6 kJ m−2. High hard-segment materials showed brittle failure with GIc

The conversion of polysaccharides into polyurethanes: A review

Abstract The conversion of polysaccharides into polyurethanes, which has commanded considerable academic and industrial interest over the past 30 years, is reviewed from chemical, structure-property and economic viewpoints. The basic chemistry of polyurethanes and the morphological structure of segmented copolyurethane materials are described. The processes used to fabricate such materials are outlined and the properties required in polysaccharides used as feedstocks for polyurethanes are defined. Several methods of incorporating polysaccharides in polyurethanes are available including their use (i) in unmodified form, (ii) after derivatisation, (iii) after depolymerisation and derivatisation, and (iv) by conversion to non-carbohydrate polyols. (Routes (ii)-(iv) yield a very wide range of glycosidic and non-glycosidic polyol structures.) Specific examples of each route and the advantages of the polyol products for use in polyurethane formation are detailed. Advantages include low cost and structural versatility of the polyols which provide increased cross-linking, and solvent and fire resistance in derived polyurethanes. Some developments in the understanding of the formation of glycosides and their industrial-scale production are presented, together with an indication of the increasing variety of polysaccharide structures used. Methodologies for the production of solid polyurethanes with high carbohydrate contents, compared to foams of relatively low carbohydrate contents, are described together with the structure-property relationships in both types of materials. Finally, the future potential of biotechnology in providing novel carbohydrate structures is briefly considered.

Synthesis and characterisation of poly(arylene sulphides)—Part 4. Curing and degradation studies

Abstract The curing and degradation behaviour of poly(phenylene sulphide) (PPS) and poly(2-methyl phenylene sulphide) (PMPS) in air and nitrogen has been studied. Curing studies have been made utilising assessment by solubility, indentation hardness, dynamic mechanical properties and heat of crystallisation studies. The results are critically discussed in terms of their ability to assess the degree of curing achieved. Degradation studies with product analysis by gas-liquid chromatography, infrared spectroscopy and chemical tests are reported and mechanisms of curing and degradation suggested and tested by studies on possible intermediates. The degradation behaviour of PMPS is complicated by oxidative and thermal reactions associated with the methyl substituent.

The thermal degradation of poly(phenylene sulphide)—Part 1

Abstract The thermal degradation of poly(phenylene sulphide) (PPS) has been studied in vacuo at temperatures between 300 and 550°C. Results indicate extensive cross-linking reactions with few degradation products at temperatures below 450°C. The products formed at higher temperatures were analysed using thermal analysis, infrared spectroscopy, mass spectrometry and gas-liquid chromatography. The major products were cyclic oligomers, dibenzothiophene and thiophenol. Mechanisms which account for these products have been suggested and discussed.

Effects of soft-segment prepolymer functionality on structure–property relations in RIM copolyurethanes

Segmented copolyurethanes comprising 40–60% by weight of polyurethane hard segments (HS) and polyether soft-segment (SS) with different functionalities (SS-fn), have been formed by reaction injection moulding (RIM). The HS were formed from 4,4′ diphenylmethane diisocyanate (MDI) reacted with ethane diol (ED). The three SS-prepolymers used were all hydroxyl-functionalised poly(oxypropylene-b-oxyethylene)s with different nominal functionalities (fn) of 2, 3 and 4 but with a constant molar mass per functional group of ∼2000 g mol−1. RIM materials were characterised using differential scanning calorimetry, dynamic mechanical thermal analysis, tensile stress–strain and single-edge notch fracture studies. Predictions using a statistical model of the RIM-copolymerisation showed that increasing SS-fn lead to more rapid development of copolymer molar mass with isocyanate conversion. Experimentally, the RIM-PU exhibited a wide range of mechanical behaviour resulting from differences in molecular and morphological structures. Increasing SS-fn produced materials with improved mould release behaviour and fracture resistance. However, increasing SS-fn also reduced the degree of phase separation developed in the copolyurethanes, resulting in increased modulus–temperature dependence and poorer tensile properties.

Synthesis and characterisation of poly(arylene sulphides)—Part 1: Poly(phenylene sulphide), poly(2-methyl phenylene sulphide) and poly(2,6-dimethyl phenylene sulphide)

Abstract A facile synthesis of poly(phenylene sulphide) (PPS), poly(2-methyl phenylene sulphide) (PMPS) and poly(2,6-dimethyl phenylene sulphide) (PDMPS) by solution polymerisation of the respective copper(I)-4-bromothiophenoxides at atmospheric pressure is described. Conditions have been optimised for the preparation of high molecular weight materials and these have been characterised prior to studies of their curing behaviour and thermal-oxidative degradation.

Polymers from renewable sources: 5. myrcene-based polyols as rubber-toughening agents in glassy polyurethanes

A reactive liquid rubber based on hydroxy-functionalized polymyrcene was used to modify a highly-crosslinked, glassy polyurethane network. During the polymerization, the products formed from the reacting liquid rubber and the polyurethane matrix components become incompatible leading to precipitation of the rubber as a discrete particulate phase. Phase-separation in the resultant rubber-modified polyurethanes is essentially complete, and the materials possess improved stress-strain and impact properties relative to the unmodified network, without reduction of the glass transition temperature (155°C) of the network. Impact data have been analysed using linear elastic fracture mechanics to give GIC, the critical strain-energy release rate. On incorporating low levels of polymyrcene liquid rubber (<10% ww) in the polyurethane matrix, GIC increased and passed through a maximum value. The mechanisms of energy dissipation accounting for the toughness changes are reviewed and compared with those observed in epoxy resins modified by polybutadiene-based liquid rubbers.

Synthesis and characterisation of poly(arylene sulphides)—Part 8: Thermogravimetry of copoly(arylene sulphides)

Abstract Poly(1,4-phenylene sulphide) (PPS), poly(2-methyl-1,4-phenylene sulphide) (PMPS) and their blends and random and block copolymers comprising 1,4-phenylene sulphide and 2-methyl-1,4-phenylene sulphide repeat units have been subjected to thermogravimetry in air and nitrogen. Comparative thermal stabilities have been evaluated and are discussed in terms of the structure and composition of the materials. The relative proportions of carbon, hydrogen and sulphur lost during char formation in nitrogen have been evaluated and related to composition.

Thermal degradation of polymers: Part XXV—Synthesis, polymerisation and thermal characterisation of m-acetamidostyrene and m-acetoxystyrene homopolymers

Abstract m-Acetoxystyrene and m-acetamidostyrene have been synthesised and homopolymerised using 2,2′-azoisobutyronitrile as free radical initiator. The resulting polymers have been characterised by a variety of methods including thermogravimetry (TG) and differential scanning calorimetry (DSC). Glass transition temperatures have been measured for samples of different molecular weight. TG and DSC have been used to compare the degradation behaviour of poly(m-acetoxystyrene) and poly(m-acetamidostyrene) with polystyrene in air and nitrogen atmospheres.

Synthesis and characterisation of poly(arylene sulphides)—Part II. Thermal analysis studies on poly(phenylene sulphide), poly(2-methyl phenylene sulphide), and poly(2,6-dimethyl phenylene sulphide) and related systems

Abstract Poly( p -phenylene sulphide), poly(2-methyl phenylene sulphide) and poly(2,6-dimethyl phenylene sulphide) have been subjected to comparative thermal analysis utilising thermogravimetry and isothermal weight loss studies in air and nitrogen. Comparative thermal stabilities have been evaluated and related to polymer structure. Activation energies for decomposition have been evaluated and are discussed. The related poly( p -phenylene sulphone) and poly(2-methyl phenylene sulphone) have also been studied and their behaviour analysed in the light of their possible formation during thermal oxidative degradation and air curing of the parent poly(phenylene sulphides).