We propose here a significantly improved process for the preparation of a lactide-clay intercalated mixture, which yields a high molecular weight (MW, M(n) similar to 126,000 Da) poly(L-lactic acid) (PLLA) clay nanocomposite (PLACN) in short times of in situ ring opening polymerization (ROP). In situ ROP using such a lactide-clay mixture enables ROP in the "nano-sized reactors" formed by the clay galleries. Cloisite (R) Na clays have been modified in-house with two different surfactant modifiers, hexadecyltrimethylammonium bromide and dioctadecyl dimethyl ammonium bromide, and these modified clays are compared with Cloisite (R) 20A and Cloisite (R) 30B. Interlayer spacings of modified clays are correlated with the resulting PLACN morphology and polymer MW growth. The optical purity of PLACNs is found similar, whereas thermal stability is significantly superior to that of neat PLLA. XRD/SAXS and TEM analyses confirm that PLACN can be prepared either with intercalated or exfoliated morphology when using either nonfunctionalized or functionalized modified clay, respectively. POLYM. ENG. SCI., 51:2066-2077, 2011. (C) 2011 Society of Plastics Engineers