Non‐isothermal crystallization behavior of stereo diblock polylactides with relatively short poly(<scp>d</scp>‐lactide) segments from the melt

<jats:title>Abstract</jats:title><jats:p>Stereo diblock polylactides (<jats:styled-content style="fixed-case">SDB‐PLAs</jats:styled-content>) composed of relatively short poly(<jats:sc>d</jats:sc>‐lactide) (<jats:styled-content style="fixed-case">PDLA</jats:styled-content>) segments and relatively long poly(<jats:sc>l</jats:sc>‐lactide) (<jats:styled-content style="fixed-case">PLLA</jats:styled-content>) segments were synthesized to have a wide number‐average molecular weight (<jats:italic>M</jats:italic><jats:sub>n</jats:sub>) range of 2.5 × 10<jats:sup>4</jats:sup>–2.0 × 10<jats:sup>5</jats:sup> g mol<jats:sup>−1</jats:sup> and <jats:sc>d</jats:sc>‐lactyl unit content of 0.9–38.6%. The effects of incorporated short <jats:styled-content style="fixed-case">PDLA</jats:styled-content> segments (<jats:italic>M</jats:italic><jats:sub>n</jats:sub> = 2.0 × 10<jats:sup>3</jats:sup>–7.7 × 10<jats:sup>3</jats:sup> g mol<jats:sup>−1</jats:sup>) on crystallization behavior of the <jats:styled-content style="fixed-case">SDB‐PLAs</jats:styled-content> were first investigated during heating after complete melting and quenching or during slow cooling after complete melting. Stereocomplex (<jats:styled-content style="fixed-case">SC</jats:styled-content>) crystallites can be formed at <jats:sc>d</jats:sc>‐lactyl unit content as low as 4.3 and 5.8% for heating and slow cooling, respectively, and for <jats:italic>M</jats:italic><jats:sub>n</jats:sub> of <jats:styled-content style="fixed-case">PDLA</jats:styled-content> segments as low as 2.0 × 10<jats:sup>3</jats:sup> and 3.5 × 10<jats:sup>3</jats:sup> g mol<jats:sup>−1</jats:sup>, respectively. With decreasing <jats:italic>M</jats:italic><jats:sub>n</jats:sub> and increasing <jats:sc>d</jats:sc>‐lactyl unit content, the cold crystallization temperature during heating decreased and the crystallization temperature during slow cooling increased. With increasing <jats:sc>d</jats:sc>‐lactyl unit content, the melting enthalpy (Δ<jats:italic>H</jats:italic><jats:sub>m</jats:sub>) of SC crystallites during heating and the crystallinity (<jats:italic>X</jats:italic><jats:sub>c</jats:sub>) of SC crystallites after slow cooling increased, whereas Δ<jats:italic>H</jats:italic><jats:sub>m</jats:sub> of PLLA homo‐crystallites during heating and <jats:italic>X</jats:italic><jats:sub>c</jats:sub> of PLLA homo‐crystallites after slow cooling decreased. The total Δ<jats:italic>H</jats:italic><jats:sub>m</jats:sub> of SC crystallites and PLLA homo‐crystallites during heating and the total <jats:italic>X</jats:italic><jats:sub>c</jats:sub> after slow cooling became a minimum at <jats:sc>d</jats:sc>‐lactyl unit content of 10–15% and gave a maximum at <jats:sc>d</jats:sc>‐lactyl unit content of 0%. Despite the accelerated crystallization of some of SDB‐PLAs, the low values of total Δ<jats:italic>H</jats:italic><jats:sub>m</jats:sub> and <jats:italic>X</jats:italic><jats:sub>c</jats:sub> at <jats:sc>d</jats:sc>‐lactyl unit content of 10–15% are attributable to the formation of two crystalline species of SC crystallites and PLLA homo‐crystallites.</jats:p>