Heat capacity data of semicrystalline poly(oxymethylene) samples. Delrin and Celcon, are analysed in order to discuss the glass transition behaviour of this polymer. There are two types of non‐crystalline poly(oxymetheylene). the mobile and rigid amorphous parts. The glass transition of the former occurs in a rather wider range of temperature: it starts at 180 K and could end at 265 K. The latter, under restraint due to the crystallites, remains frozen up to the melting temperature.

The microwave‐assisted direct polycondensation of LA to synthesize PLA has been studied. Microwave irradiation strikingly accelerates the polymerization rate of LA compared to conventional heating. By use of a binary catalyst of SnCl2/p‐TsOH, PLA with a $\overline M _{\rm w}$ of 16 000 is obtained within 30 min under a reduced pressure of around 30 mmHg. MALDI‐TOF MS measurements reveal that the PLA formed is mainly composed of linear polymer and macrocyclics.

The effects of addition of neutral salts on the cholesteric mesophase structure and optical properties of aqueous solutions of hydroxypropyl cellulose (HPC) were investigated by spectrophotometry and an NMR technique with D 2 O as solvent. In the measurements of selective light-reflection spectra, the wavelength of maximal reflectance and therefore the cholesteric helical pitch (P), too, varied systematically with a change in strength of a socalled "chaotropic" effect of the additive salts; i.e., their effectiveness in increasing P was pronounced in the order of Cl −

The heat capacities of 38 semicrystalline poly(oxymethy1ene)s and poly(oxyethy1ene)s were determined by differential scanning calorimetry from 205 K through the melting transition. By comparison with the well known limiting heat capacities of the supercooled liquids and the crystals of the macromolecules it was found that there are negative and positive deviations from additivity of the heat capacities with crystallinity between the glass transition and the melting transition. The negative deviations are linked with "rigid amorphous" material, and the positive deviations were previously linked to defect formation or early melting. The rigid amorphous fraction in poly(oxymethy1ene) is constant up to the melting region, in contrast to polypropylene, where it is decreasing with temperature. The proposed mesophase transition in poly(oxymethylene) is shown to be a minor effect. The poly(oxyethy1ene) heat capacity is governed by positive heat capacity deviations within the rather short temperature range between glass transition and melting.

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