Effects of Reaction Temperature on the Formation of Polyurethane Prepolymer Structures

Abstract

For the first time, the molecular weight distribution and extent of side reactions have been quantified in polyurethane prepolymers. A combination of NMR, size exclusion chromatography, and mass spectrometry has been used to measure the molecular weight distribution. The values obtained are consistent with Flory's step polymerization theory. The type and amount of side reactions as a function of reaction temperature have also been investigated. At low temperature of reaction, the amount of branches arising from allophanate linkages is negligible. With only a relatively modest change in reaction temperature, this type of side reaction increases dramatically, so that at 145 °C as much as 10% of the nitrogens participate in allophanate linkages. The effect of this reaction on the molecular weight distribution was also measured. Upon formation of these side products, the molecular weight distribution broadens and the average increases. In this prepolymer system, the reactivity is independent of molecular weight.

Effect of isocyanate index on the properties of rigid polyurethane foams blown by HFC 365mfc

“…Consequently, the use of environmentally friendly blowing agents has become an important and urgent issue in the synthesis of polyurethane foam. [12][13][14] Water can in part replace such environmentally hazardous blowing agents. However, the excessive use of water causes a negative pressure gradient due to the rapid diffusion of CO 2 through the cell wall causing cell deformation.…”

Review on the Functional Determinants and Durability of Shape Memory Polymers

“…In segregated shape memory polyurethanes (SMPUs), the sharpness of the glass transition is dependent on the degree of phase mixing; an increase in phase mixing normally results in the broadening of a glass transition. Factors that control the degree of phase separation include copolymer composition, block length (molecular weight), crystallinity of segments, synthesis conditions and thermal history [66][67][68].…”

Modulation of cavities and interconnecting pores in manufacturing water blown flexible poly (urethane urea) foams

“…The allophanate and biuret bonds can be produced as side products under catalyst conditions only in the presence of excess amount of the isocyanate through the reaction process. 3,9,10 In fabrication of flexible PUU foams, the most important characteristic is to have open structured cavities and interconnecting pores. In PUU foams, the hard segments (rigid blocks: aromatic rings from isocyanate) located in the urethane and urea groups have strong polarity to bring about thermodynamic incompatibility with soft segments (soft blocks: carbon chains from polyol).…”